Method of measuring the potential difference across a conductive sheet material for controlling the pickling of said sheet



Nov. 12, 1968 c. VAN DEN HOVE 3,411,082

METHOD OF MEASURING THE POTENTIAL DIFFERENCE ACROSS A CONDUCTIVE SHEET MATERIAL FOR CONTROLLING THE PICKLING OF SAID SHEET Filed Dec. 12, 1965 3 Sheets-Sheet 1 27 OSCILLOSCOPE 2/ 2 3 7 4 SPEED 60 CONTROL Nov. 12, 1968 c VAN DEN HOVE 3,411,082

METHOD OF MEASURING THE POTENTIAL DIFFERENCE ACROSS A CONDUCTIVE SHEET MATERIAL FOR CONTROLLING THE PICKLING OF SAID SHEET Filed Dec. 12, 1965 3 Sheets-Sheet 2 23 A) OSCILLOSCOPE 22 L|:- 24

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Nov. 12, 1968 c. VAN DEN HOVE 1,082

METHOD OF MEASURING THE POTENTIAL DIFFERENCE ACROSS A CONDUCTIVE SHEET MATERIAL FOR CONTROLLING THE PICKLING OF SAID SHEET Filed Dec. 12, 1963 3 Sheets-Sheet 5 J4 J4 34 3g.

jig/0 United States Patent 3,411 082 METHOD OF MEASURING THE POTENTIAL DIF- FERENCE ACROSS A CONDUCTIVE SHEET MA- TERIAL FOR CONTROLLING THE PICKLING OF SAID SHEET Christian Van Den Hove, Bressoux, Belgium, assignor to Centre National de Recherches Metallurgiques, Brussels, Belgium Filed Dec. 12, 1963, Ser. No. 330,086 Claims priority, application Belgium, Dec. 20, 1962, 39,638, Patent 626,376 7 Claims. (Cl. 324-65) ABSTRACT OF THE DISCLOSURE This specification discloses a method and apparatus for the control of the descaling of a metallic sheet passing continuously through a pickling bath, wherein the presence or absence of scaling is detected by placing a pair of electrodes in contact with the sheet at spaced locations and recording the potential difference between them when a current flows, and wherein the speed of passage of the sheet through the bath is controlled in order to achieve the dseired degree of descaling at the location of the electrodes.

In modern installations for the removal of scale oxide from strips of steel sheet, the steel sheet is usually passed through successive baths of pickling solution until its surface is clean enough for the use for which it is intended.

One disadvantage of the process in its present form is that there are considerable variations in the thickness and nature of the scale oxide layer on it. It has been found impossible to produce the sheet in such a fashion that the scale oxide layers on ditferent batches of steel sheet require the same treatment time in pickling solution. Therefore it is necessary to vary the speed at which the steel sheet passes through the various baths of pickling solution. Though the setting of the speed of the steel sheet as it passes through the baths at such a value as to achieve complete pickling without causing undue etching of th sheet does not require an extremely high degree of skill of the opeartor, the use of visual control has in fact in practice been found to lead to bottle necks in the production line.

The present invention has been devised more particularly for overcoming this difficulty.

The present invention therefore consists in a method of measuring the thickness of an electrically resistant film on a band of conductive material undergoing treatment in a liquid to remove the film. In the method in accordance with the invention the band is contacted by a pair of electrodes and the potential difference between the electrodes is measured.

The invention has been found particularly applicable to the pickling of steel sheet. In a conventional process for carrying out this pickling process continuous bands or strips of the steel sheet are passed successively through a number of pickling baths or vats. In order to make the invention clear a specific embodiment of it as applied to the pickling of steel sheet in continuous bands will now be described with reference to the attached drawings.

FIGURE 1 is a diagrammatic vertical section showing the passage of steel sheet through four consecutive baths.

FIGURE 2 is a side view of an electrode support for use in the method in accordance with the invention.

FIGURE 3 is a plan view, in a scale somewhat less that that of FIGURE 2, showing the movement of the electrode support.

FIGURE 4 is a plan view of the end piece of the 3,411,082 Patented Nov. 12, 1968 "ice electrode support shown in FIGURE 2, the scale being greater than the scale of FIGURE 2.

FIGURE 5 is an electrical diagram showing the connection of the electrodes.

FIGURES 6, 8 and 9 show diagrammatically the engagement of the steel sheet by the electrodes.

FIGURE 7 shows a trace of electrical signals received from two sets of electrodes.

FIGURES 10 and 11 show further traces received from two sets of electrodes.

As shown in FIGURE 1, steel sheet 5 which has just been rolled after coming from a series of rolling mills, passes in the direction indicated by arrow 6 consecutively through pickling baths 1, 2, 3 and 4 drawn by a pair of drive rolls 6a having a speed control 6b, and then onto a take-up reel 6c. At the positions indicated by reference numerals 7 and 8, that is to say between the last and next to last bath and after the last bath, electrodes 19 for sensing the thickness of the film scale oxide are placed.

As shown in FIGURE 2 and FIGURE 3 the electrodes 19 are carried in pairs at the end of electrode supports 13. Each electrode support 13 has an end piece 14 (see FIGURE 4) in which the electrodes 19 are mounted in vertical holes 15. The electrode support 13 has an upright portion 10 which is mounted in two bearings 11 on a firmly mounted vertical part 9. A gear wheel 12 is keyed on the portion 10 and this gear wheel 12 is driven by a worm (not shown) driven in turn by an automatic mechanism which causes the portion 10 of the electrode support 13 to oscillate about a vertical axis. The automatic mechanism includes limit switches 18 (see FIG- URE 3) which cause the electrode support 13 to be reversed as soon as it has reached one of the extreme positions shown in broken lines radiating from the axis of the part 10. The total angular movement or sweep of the electrode support 13 is somewhat greater than the width of the band of sheet steel 5. The band of sheet steel 5 is somewhat narrower than the baths and can wander from side to side somewhat. The total sweep of the electrode support 13 is indicated by the broken line 17.

In order to prevent a film of pickling solution interfering with the electrical contacts between the electrodes 19 on the one hand, and the band of sheet metal, on the other hand, there is provided a jet 27 mounted in a vertical hole 28 in the end piece 14 of the electrodes support 13. Compressed air is supplied to the jet 27 through a flexible tube 26 and the horizontal pipe 25.

The two electrodes 19 are, as shown in FIGURE 5, connected with a 1.5 volt DC source 22 of electricity. The voltage across the electrodes 19 is amplified at 23 and fed to a visual indicator 24 such as an oscilloscope or strip recorder.

If the pickling is sufficient to cause the band 5 of sheet steel to be completely devoid of scale oxide where it is contacted by a pair of electrodes 19 (see FIGURE 6) the trace produced at 24 will be as shown by trace 29 in FIGURE 7. In FIGURE 7 the horizontal axis represents time and the vertical axis represents voltage. The portions 31 of the trace 29 correspond to the positions of the electrodes 19 in which the electrodes are not both in contact with the sheet, i.e. the extreme positions indicated by broken lines radiating from the axis of part 10 in FIGURE 3. The parts-33 of the trace 29 indicate that the electrodes 19 are both in contact with the band ;5 and therefore the voltage across the electrodes 19 is The trace 29 is FIGURE 7 indicates the operation of the electrodes placed at the positions 7 in FIGURE 1 while the similar trace 30 in FIGURE 7 indicates the operation of the electrodes placed at position 8 in FIG- URE 1. It will be seen from FIGURE 7 that the trace 30 has portions 34 and 32 corresponding respectively to the portions 33 and 31 of trace 29.

However if the apparatus operates so that the traces are as shown in FIGURE 7, there will be the disadvan tage that the metal will be more or less completely clean at position 7 and bath 4 will merely serve to cause an excessive pickling or in any case will serve no useful purpose. The operator will therefore adjust the speed of the band 5 by controlling the speed of the rolls 6a along the speed control 671, until the traces are as shown in FIGURE 11. In this case at position 7 the electrodes will make extremely imperfect contact with the metal band 5 and the jagged portions of the trace 29 at-39 will result. This will be caused by the presence of scales of scale oxide 43 on the surface of the band 5 as shown diagrammatically in FIGURES 8 and 9. Thus in FIGURE 8 one electrode 19 is touching the band 5 and another is touching the top of a piece of film 43 so that the voltage between the electrodes 19 will be less than in the situation shown in FIG URE 9 in which neither of the electrodes are able to con tact the band 5. On the other hand, if the apparatus is run so that the traces obtained are as shown in FIGURE 11 the metal will be substantially clean at position 8 but will still have a substantial layer of film at position 7. Therefore the passage through the bath 4 will not be wasted.

FIGURE shows the case where the passage of the metal through the apparatus is altogether too fast and the filmleft on it at position 8 prevents the electrodes making adequate contact with it to produce level parts 34 of the trace 30.

Various modifications can be made in the apparatus. For example the electrodes can be insulated except at their tips and can be arranged to contact the sheet metal while it is actually below the level of the liquid in one of the baths.

It is possible to connect e.g. weld a series of sheets of metal together for treatment in the apparatus so as to form a band, instead of using the apparatus to treat a single band formed in the one piece.

In practice it has been found advantageous to place a pair of electrodes so as to contact the sheet as it emerges from each of the'baths of pickling solution. The adjustment of the speed of the sheet is then made as a statistical function of all'the signals received from the electrodes.

This is especially useful when different sheets of metal are temporarily welded together so as to form a band since if, for example, the nature of a sheet only extending to a position just downstream from the first bath is such that it is'completely clean as it emerges from the bath, the line of sheets can at once be speeded up in order to prevent damage to the first sheet. If there is only one.pair.of electrodes between the last and next to last baths and a further pair of electrodes downstream from the last bath, this would not be possible since the sheet would have to pass through the second and third baths before the fact that 'it was completely clean was noted.

Instead of providing electrodes which sweep across the width of the sheet a series of fixed sensing devices with electrodes can be arranged in a' row across the sheet for measuring the-potential difference at a given position.

The process forming the object' of the invention is especially advantageous when it is used in conjunction with a continuous rolling 'mill.

It has been found1that the application of the invention enables a single row of pickling baths to be used to deal with an output that would normally necessitate the use of two rows of picklingbaths. 7

As a further modification of the method in accordance with'the invention is is possible to compare the potential difference between the electrodes with that obtained when they are applied to'a standard sample of sheet metal With a clean surface.

While I have described one embodiment of my invention in order that those skilled in the art may take full advantage of it, it is to be understood that the embodiment has been .only by way of illustration and is in no sense to be taken to limit'the scope of the monopoly I claim in the United States. This monopoly is to be determined in accordance with the spirit and gist of the following patent claims.

I claim:

1. A method of controlling the pickling of a sheet material comprising the steps of: continuously moving an oxide covered metallic sheet'through at least one pickling bath at a controlled speed; applying a pair of electrodes to the surface portion of said sheet emerging from the pickling bath; applying an electric current source to said electrodes; continuously measuring the potential difference between the electrodes while the remaining sheet portion moves through the pickling bath; protiding a source of reference potential difference representing a sheet suitably pickled; comparing and recording said measured potential difference with said reference potential difference; and adjusting the controlled speed of the movement of said sheet through the pickling bath to bring the measured potential difference into line with that of the reference potential difference.

2. A method as claimed in claim 1, further comprising the step of subjecting the electrodes to an oscillatory motion transversely of the sheet while remaining in contact with the sheet.

3. A method as claimed in claim 1, further comprising the step of directing a jet of air onto the sheet immediately ahead of the zone of contact with the electrodes.

4. A.method as claimed in claim 1, wherein the step of continuously moving said sheet further comprises the step of continuously. moving said sheet through a succession of pickling baths, and wherein the step of applying said pair of electrodes further comprises the step of applying said pair of electrodes between two of the baths.

5. A method as claimed in claim 4, wherein the step of providing a reference potential difference comprises the steps of: applying a further pair of electrodes to the surface of said sheet after it has left the last bath; and applying a further electric current source to said electrodes, whereby a source of reference potential ditference is provided between said further pair of electrodes.

6. A method as claimed in claim 5, further comprising the step of subjecting the electrodes to an oscillatory motion transversely of the sheet while remaining in contact with the sheet.

7. A method as claimed in claim.5, further comprising the step of directing a jet of air onto the sheet immediately ahead of the zone of contact with the electrodes.

References Cited UNITED STATES PATENTS 1,623,436 4/1927 Peschl 324- X 1,815,915 7/1931 Kallander 324-65 X 1,976,487 10/1934 Elberty 324-65 X 2,146,442 2/1939 Price' 324-61 X 2,484,594 10/1949 Spangenberg 324-65 X 2,545,576 3/1951 Godley 324-65 X 2,793,345 5/1957 Hags 118-6 X 2,797,171 6/1957 Fralish 118-9 X 2,811,691 10/1957 Dahm et a1 324-65 2,883,895 4/1959 Vossberg 118-6 X 2,927,871 3/1960 Mancke et al. 134-57 X 2,942,352 6/ 1960 Eicken-Estienn 324-65 X 3,086,889 4/1963 Strong 118-8 3,129,712 4/1964 Thomas 134-57 FOREIGN PATENTS 761,241 11/1956 Great Britain.

RUDOLPH V. ROLINEC, Primary Examiner.

E. E. KUBASIEWICZ, Assistant Examiner. 

